Corneal Ulcers

Q:I was wondering about corneal ulcers. I have a 30-year-old horse that has lost eyesight in one eye from age, and I am treating him now for a corneal ulcer. I read your article on eye problems (November 2010 issue) and was wondering what medications are usually used for treating this problem. I know I am using (antibiotics) neomycin and polymyxin B and bacitracin, zinc ointment, and atropine sulfate. He is doing great, but I rarely read much about treatment for this problem.

Lucy Smith, via e-mail

A: Once a corneal ulcer is diagnosed, the therapy must be carefully considered to ensure comprehensive treatment. Medical therapy almost always comprises the initial major thrust in ulcer control, albeit tempered by judicious use of adjunctive surgical procedures. This intensive pharmacological attack should be modified according to its efficacy. Subpalpebral (beneath the eyelid) or nasolacrimal (tear drainage) lavage treatment systems can be employed to treat a fractious horse or one with a painful eye that needs frequent therapy. The clarity of the cornea, the depth and size of the ulcer, the degree of corneal vascularization (blood supply), the amount of tearing, the pupil size, and the intensity of the anterior uveitis (inflammation of the iris and ciliary body, which is a muscular ring located in the front part of the eye) should be monitored. Serial fluorescein dye staining of the ulcer is indicated to assess healing. Self-trauma should be reduced with hard or soft cup hoods (that protect the eye).

Bacterial and fungal growth must be halted and the microbes rendered nonviable. Broad-spectrum topical antibiotics are usually administered with culture and sensitivity tests aiding selection. Topically applied antibiotics, such as chloramphenicol, bacitracin-neomycin-polymyxin B, gentamicin, ciprofloxacin, cefazolin, or tobramycin ophthalmic solutions, may be used to treat bacterial ulcers. Voriconazole, miconazole, and natamycin are often used for topical treatment of fungal ulcers.

Severe corneal inflammation secondary to bacterial (especially, Pseudomonas and beta-hemolytic Streptococcus) or, much less commonly, fungal infection may result in sudden, rapid corneal liquefaction and perforation. Activation and/or production of proteolytic enzymes by corneal epithelial cells (those in the lining of blood ves-sels), leukocytes (white blood cells), and microbial organisms are responsible for stromal collagenolysis or "melting." Autogenous (generated in the body) serum administered topically can reduce tear film and corneal protease (which breaks proteins down into amino acids) activity in corneal ulcers in horses. The serum (which is produced by spinning down the patient's own blood) can be administered topically as often as possible and should be replaced by new serum every five to 10 days. Five to 10% acetylcysteine and/or 0.05% sodium EDTA (ethylenediaminetetraacetate) can be instilled hourly, in addition to the other indicated drugs, for anti-melting effect until stromal liquefaction (melting) ceases.

Atropine sulfate is a common therapeutic agent for equine eye problems. Topically applied atropine (1%) is effective in stabilizing the blood-aqueous barrier (that prevents exchange of materials between the chambers of the eye and the blood), reducing vascular protein leakage, minimizing pain from ciliary muscle spasm, and reducing the chance of synechia formation (a disease of the eye in which the iris adheres to the cornea or the capsule of the crystalline lens) by causing pupillary dilation.

Systemically administered NSAIDs such as phenylbutazone (Bute) or flunixin meglumine (Banamine) can be used orally or via injection and are effective in reducing uveal exudation (oozing) and relieving ocular discomfort from the anterior uveitis in horses with corneal ulcers.

Horses with corneal ulcers and secondary uveitis should be on stall rest until the condition heals. Intraocular hemorrhage and increased severity of uveitis can result from overexertion.

About the Author

Dennis E. Brooks, DVM, PhD, Dipl. ACVO, is a professor of ophthalmology at the University of Florida. He has lectured extensively, nationally and internationally, in comparative ophthalmology and glaucoma, and has more than 140 refereed publications. He is a recognized authority on canine glaucoma, and infectious keratitis, corneal transplantation, and glaucoma of horses.

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